I could serve you could serve he could serve we could serve you could serve they could serve
V-ing form
I could be serving you could be serving he could be serving we could be serving you could be serving they could be serving
Perfect
I could have served you could have served he could have served we could have served you could have served they could have served
V-ing perfect
I could have been serving you could have been serving he could have been serving we could have been serving you could have been serving they could have been serving
Negation
Simple form
I could not serve you could not serve he could not serve we could not serve you could not serve they could not serve
V-ing form
I could not be serving you could not be serving he could not be serving we could not be serving you could not be serving they could not be serving
Perfect
I could not have served you could not have served he could not have served we could not have served you could not have served they could not have served
V-ing perfect
I could not have been serving you could not have been serving he could not have been serving we could not have been serving you could not have been serving they could not have been serving
Interrogative form
Simple form
could I serve? could you serve? could he serve? could we serve? could you serve? could they serve?
V-ing form
could I be serving? could you be serving? could he be serving? could we be serving? could you be serving? could they be serving?
Perfect
could I have served? could you have served? could he have served? could we have served? could you have served? could they have served?
V-ing perfect
could I have been serving? could you have been serving? could he have been serving? could we have been serving? could you have been serving? could they have been serving?
Interro-negative form
Simple form
could I not serve? could you not serve? could he not serve? could we not serve? could you not serve? could they not serve?
V-ing form
could I not be serving? could you not be serving? could he not be serving? could we not be serving? could you not be serving? could they not be serving?
Perfect
could I not have served? could you not have served? could he not have served? could we not have served? could you not have served? could they not have served?
V-ing perfect
could I not have been serving? could you not have been serving? could he not have been serving? could we not have been serving? could you not have been serving? could they not have been serving?